The myocardial oxygen consumption measurement (MvO2; cc/min/100g) serves to approximate the energy utilization of the heart. Knowing the oxygen consumed per unit time would permit an assessment of the energy costs of several mechanical aspects of left ventricular contraction. Such information would appear fundamental to regulating energy utilization in the acutely ischemic heart, thereby maintaining cell viability and controlling infarct size. The immediate aim of the project is to elucidate the energy costs accompanying the development (rate and extent) and maintenance of left ventricular wall force under normal and coronary flow-limited conditions. For this purpose MvO2 was continuously monitored in an isolated, servo-regulated canine heart preparation; only the steady state response in MvO2 to mechanical pertubations was analyzed. Results to date indicate 1) right ventricular force development did not influence MvO2. This was determined for RV filling pressures of O-32 mm Hg with the LV empty or contracting isovolumically from filling pressures of 0-32 mm Hg; 2) MvO2 was a function of LV developed force (r more than 0.9); 3) the MvO2 of ejecting beats was, on the average, 45% greater than isovolumic, matched developed force counterpart. This increment in MvO2 was determined by ejection force (p less that 0.02) and not the extent of shortening; 4) for matched levels of developed force MvO2 was greater during dobutamine infusion. The increment in MvO2 reflecting the degree of augmentation in the rate of force development and thereby drug related increments in contractile state concentration; and therefore 5) for any given contractile state or rate of force development MvO2 was a function of both developed and maintained force (integral of systolic force, r more than 0.9). BIBLIOGRAPHIC REFERENCES: Weber, K.T., Janicki, J.S., Reeves, R.C. Hefner, L.L. Factors influencing left ventricular shortening in isolated canine heart. Am.J.Physiol. 230:419-426, 1976. Weber, K.T., Janicki, J.S., Hefner, L.L. Force-length relations of isovolumic and ejecting contractions. Am.J.Physiol. 231:(In press, Aug. 1976).